Is a Directional/Flow Map Necessary for Hair Cards?
Stumbled on this while looking for a way to vector field flow in blender... While I'm here
&quot;I read on other forums that creating a flow map may not be necessary if the UV's are all unwrapped and flowing in the same direction, is that correct?&quot;
No. Absolutely not.
If you bend the hair cards in your particle, it matters not where the UV goes, the flow of the normals is impacted and different engines (namely unreal) will render stuff differently.
What the flow map is, for hair cards, is a fixed world normal texture that covers each individual hair card. So you need to create an additional UV in blender, smart UV unwrap, and bake world normals.
You can then play with the texture paint tool and some visual balancing to adjust the flow look manually - a bit tedius. Usually use the smudge tool.
The shader, is than told to use this map with UV coord 1 to derive normals and tangent. making the hair appear to bend more appropriately.